This invention relates to equalization of magnetic tape signals, and, more specifically, to adjusting the equalizer of magnetic tape drives.
The read waveform of a magnetic recording channel requires filtering prior to read detection to shape it. This filter is called an equalizer.
The magnetic write and read heads are typically formed by thin film processes which have a range of acceptable tolerances such that the transfer functions differ to some extent, and so that no one equalization filter matches all heads. Therefore, equalization filters typically are arranged to match a particular head.
Typically, one or more of multiple iterative algorithms are employed to initialize an equalization filter, such as a least mean squares (LMS) algorithm, using the waveform of a special test pattern or using data as the signal to which the algorithm is applied. A drawback of this method is that it requires many iterations to converge. The LMS approach is discussed with respect to data communication in xe2x80x9cPrinciples of Data Communicationxe2x80x9d, R. W. Lucky et al., McGraw-Hill, New York, 1968, pp. 156-165. As another example, a Zero Forcing (ZF) algorithm could be used.
The special test pattern may comprise an equalizer training sequence applied to an equalizer filter at manufacture of the tape drive by a special test tape, which may comprise a pseudo-random binary sequence (PRBS), which contains repetitions of combinations of signals, so that an LMS algorithm may set the equalizer filter.
An equalizer training sequence, for example, may be supplied on the special test tape, and, as another example, as a special calibration pattern written at a specified location of a data tape, such as discussed in U.S. Pat. No. 6,366,418, McEwen et al. If employed as a repeated calibration pattern on a data tape, the equalizer training sequence might occupy a significant length of the magnetic tape, detracting from the amount of data that would otherwise be stored.
The LMS algorithm relies upon tentative decisions to be made on the pseudo-random training data, or the random data waveforms, which typically causes the algorithm to converge on a correct transfer function, but with enough noise, these decisions can be erroneous, causing the algorithm to diverge with improper updates to the equalizer taps.
The present invention comprises a method and system for a magnetic tape drive, implemented as hardware logic or as a computer program product usable with a programmable computer processor having computer readable program code embodied therein, for adjusting an adjustable read detection equalizer filter of a read detection system for a magnetic tape drive.
As known to those of skill in the art, magnetic tapes are arranged with standardized formats, typically with various recording format required control pattern signal fields throughout the magnetic tape. For example, a Linear Tape Open (LTO) magnetic tape will be recorded with a sync mark, a VFO field (variable frequency oscillator), and a data set separator field (DSS) between data sets.
In one embodiment of the present invention, a control processor is responsive to at least a portion of a required control pattern signal sensed from a magnetic tape by the magnetic read head, the required control pattern signal comprising a required portion of a normal recording format of the magnetic tape. The control processor processes the sensed required control pattern signal with respect to a target reference pattern signal to adapt the read detection equalizer filter to the target.
In a further embodiment, the required control pattern signal comprises a pattern of signals outside the normal encoded data detection of the magnetic tape drive. An example comprises the data set separator (DSS) signal, also called an interblock gap signal, discussed above. A control pattern recognition sensor of the system for recognizing the required control pattern signal, additionally triggers the control processor to respond to the sensed required control pattern signal. In an embodiment related to an example of a DSS signal, the control pattern recognition sensor recognizes at least one signal of a greater time period than a maximum time period of normal encoded data detection of the magnetic tape drive, as being the required control pattern signal. In an embodiment related to another example of a data set separator signal, the control pattern recognition sensor recognizes a sequence of signals outside normal encoded data detection of the magnetic tape drive, as being the required control pattern signal.
In another embodiment, the control processor additionally cancels baseline distortion of the sensed required control pattern signal. In one example, the control processor cancels the baseline distortion of the sensed required control pattern signal by conducting cosine compensation of the baseline distortion.
In a still further embodiment, wherein the required control pattern signal is repeated at a plurality of locations of a magnetic tape read by the magnetic tape drive, the read detection system additionally comprises an error detector for detecting that reading of data of a magnetic tape exceeds a read error trigger. As the result of an error trigger, a selection is made of at least one required control pattern signal, which may have already been captured, in close proximity to the data detected as exceeding the read error trigger. In another embodiment, wherein the read detection equalizer filter comprises adjustable presets, the control processor temporarily adapts the read detection equalizer filter from those presets. In a further embodiment, the control processor additionally resets the read detection equalizer filter to the presets for a magnetic tape subsequently loaded in the magnetic tape drive.
In still another embodiment, wherein a loading detector is provided for detecting loading of a magnetic tape in the magnetic tape drive, operation of the control processor to respond to the sensed required control pattern signal is initiated in response to detecting loading of a magnetic tape. Still further, each encountered required control pattern signal triggers adaption of the read detection equalizer filter.
In a further embodiment, the control processor responds to time based digital samples of the required control pattern signal; and directly adapts the read detection equalizer filter employing the time based digital samples and the target reference pattern signal. In another embodiment, the control processor additionally rotates a minimum slope point of a signal vector of the sensed required control pattern signal to an end of the signal vector and sets the minimum slope point to zero.
In a further embodiment, the control processor responds to digital samples of magnetic transitions of the required control pattern signal; and additionally averages similar digital samples of the magnetic transitions within a window comprising a plurality of the magnetic transitions.
For a fuller understanding of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.